1. Field of the Invention
The present invention relates to a disk device in which a recording head is moved while a disk as a recording medium is rotated so that information is recorded on and/or reproduced from the disk. More particularly, the present invention relates to a disk device having a temperature control mechanism for suppressing a temperature rise.
2. Description of the Related Art
In a disk device of the above type, an operation called a seek, which involves moving a recording head to a predetermined position at high speed, is frequently repeated in some cases. Such a seek consumes an extremely large amount of power when compared with a normal recording and/or reproduction operation which does not include high-speed movement of the head. Accordingly, if seeks are continuously performed for an extended period of time, the temperature inside the disk device becomes high. In the case where the disk is under control by constant angular velocity (CAV), such heating during the seek mainly arises from a motor driving system for moving the head. In the case where the disk is under control by constant linear velocity (CLV), the heating during the seek mainly arises from a motor driving system for driving the disk, in addition to the motor driving system for moving the head.
Due to such a temperature rise caused by the heating of the driving system during the seek, the temperatures of the disk and components of the disk device exceed their respective allowable temperature levels.
Some measures for overcoming the above problem of temperature rise have been proposed. For example, U.S. Pat. No. 5,566,077 discloses a construction in which a temperature sensor is provided inside an optical disk devise for detecting the temperature of the device so as to limit the operation of the device when the temperature of the device exceeds a predetermined temperature level thereby preventing an excessive temperature rise.
A technique has also been proposed in which the temperature at a desired position is predicted by an arithmetic operation. According to this technique, the cost and the number of assembling steps can be reduced since installation of a temperature sensor is not required. Also, the temperature of a position at which direct installation of a temperature sensor is difficult can be obtained. For example, Japanese Laid-Open Publication No. 7-153208 discloses a construction in which temperature rise of a voice coil motor (VCM) for moving a head is predicted by an arithmetic operation based on a current instruction value for the VCM.
FIG. 5 shows an example of a conventional disk device which predicts a temperature rise by an arithmetic operation.
Referring to FIG. 5, a conventional magnetic disk device 101 includes a disk enclosure (DE) 102. The DE 102 includes a disk motor 103, a spindle 104, a voice coil motor (VCM) 106, and a magnetic head 107. A magnetic disk 105 is loaded in the DE 102. The VCM 106 moves the magnetic head 107 in a direction of the radius of the magnetic disk 105 for positioning the magnetic head 107. The magnetic disk device 101 further includes a servo controller 118, which includes a VCM control section 135. The VCM control section 135 includes a temperature detection sub-section 114 for predicting the temperature of the VCM 106, a positioning control sub-section 115, and RAM 122.
The RAM 122 stores data, such as a VCM current instruction value Iv, the quantity of heat corresponding to a temperature rise xcex94Qv1, the quantity of heat corresponding to spontaneous heat emission xcex94Qv2, the quantity of heat of an object to be measured Qv, and the temperature of the object to be measured Tv, renewably. The RAM 122 is provided with a soft timer. In addition, ROM (not shown) prey stores data such as a constant K, a constant indicating heat resistance xcex8, the heat capacity of the object to be measured Cv, the environmental temperature Ta, the sampling time ts, a constant a, and a constant b.
In the magnetic disk device 101 with the above configuration, the temperature detection sub-section 114 performs a prediction operation of the temperature of the VCM in the following procedure.
The VCM control section 135 interrupts normal seek control every sampling time ts of 66 xcexcsec, to detect the position of the magnetic head 107 and renew the VCM current instruction value Iv. Then, the temperature detection sub-section 114 multiplies the second power of the VCM current instruction value Iv by the coefficients K and ts to obtain the quantity of heat corresponding to temperature rise of the object to be measured xcex94Qv1 (=Iv2xc3x97Kxc2x7ts). A value obtained by subtracting the quantity of heat corresponding to the spontaneous heat emission of the object to be measured xcex94Qv2 from the quantity of heat corresponding to temperature rise xcex94Qv1 is then integrated (Qv←Qv+xcex94Qv1xe2x88x92xcex94Qv2), so as to obtain the quantity of heat of the object to be measured Qv and thus detect the temperature of the object to be measured Tv (Tv=Qv/Cv).
The above processing is performed every sampling time ts and the detected temperature Tv is stored in the RAM 122. During a seek, the temperature Tv is read from the RAM 122 to perform seek control based on the temperature Tv.
In the seek control, if the detected temperature Tv is larger than a reference value, the start of the seek is delayed depending on the temperature Tv, so that temperature rise is suppressed.
A delay amount D by which the start of the seek is delayed is set as a primary function of the temperature Tv at D=aTvxe2x88x92b (wherein a and b are constants stored in the ROM). The delay amount D is set depending on the temperature Tv in the following manner: When the reference value for the temperature Tv is T1, the delay amount D is set at 0 if Tvxe2x89xa6T1 and set at aTvxe2x88x92b if Tv greater than T1.
Accordingly, the seek is started upon receipt of a seek instruction if the temperature Tv is less than the reference value T1, or the seek is started only after a delay by the delay amount D which is proportional to the temperature Tv if the temperature Tv exceeds the reference value T1. This suppresses the temperature rise of the VCM and thus prevents an occurrence of overheating and breaking of the VCM.
The above conventional disk device has the following problems.
The first problem is that the amount of the arithmetic operation required for the temperature prediction is large. Accordingly, the control section must bear a large burden. More specifically, for the temperature prediction operation, the control section must perform interruption at a very frequent sampling period of 66 xcexcsec. For each interruption, the control section retrieves the current instruction value Iv and performs calculations for obtaining the quantity of heat xcex94Qv1, the quantity of heat radiation xcex94Qv2, and the temperature Tv. This interruption is required all the time irrespective of whether the device is under the recording operation or the seek operation. Such frequent interruption significantly increases the burden on the control section of the disk device, lowering the processing capability of the control section.
The second problem is as follows. While the temperature of the VCM is controlled so as not to exceed its allowable temperatures, it has been found that the difference between the temperature of the center of the disk and the ambient temperature, not the temperature of the disk itself, is important in specific cases. Such a specific case includes the case in which a disk is warped when the disk motor is heated. When the disk motor is heated, the inner circumference of the disk which is closer to the disk motor is heated more than the outer circumference of the disk causing a temperature gradient over the inner and outer circumferences of the disk. If the entire disk is heated uniformly, the disk will have little deformation, However, if the disk has a temperature difference between portions thereof, the disk is warped. Warping of the disk results in an increase in the aberration of an optical spot formed on the disk by an optical beam emitted from an optical head and thus a reduction in the reliability of recording and/or reproduction. Such differences between the portions of the disk are not conventionally detected and thus fail to effectively prevent warping of the disk.
An object of the present invention is to provide a disk device requiring a reduced amount of arithmetic operation and thus reducing the burden on a control section.
Another object of the present invention is to provide a disk device which performs temperature control capable of suppressing warping of a disk with high precision.
The disk device of this invention includes: a disk driving section for rotating a disk; a head for recording and/or reproducing information on and/or from the disk; a head moving section for moving the head from a start position to a destination position; a temperature calculation section for calculatlng a temperature change at a predetermined position, wherein the calculation is carried out based on the information of the start position and the destination position; and a control section for controlling the disk driving section and/or the head moving section depending on the temperature change calculated by the temperature calculation section.
In one embodiment of the invention, the temperature calculation section includes a timer, a heat value calculation sub-section, and an accumulation sub-section, wherein the timer starts counting lapse time from a point when the preceding temperature change has been calculated, the heat value calculation sub-section calculates a heat value of the disk driving section and/or the head moving section generated by the movement of the head from the start position to the destination position, and the accumulation sub-section calculates the temperature change based on the preceding temperature change, the lapse time, and the heat value and renews the temperature change.
In another embodiment of the invention, the timer counts a lapse time t defined as from a point when an (nxe2x88x921)th temperature change has been calculated until a point when an n-th temperature change is calculated, wherein the heat value calculation sub-section calculates a heat value E as the heat value generated during the lapse time t, and the accumulation sub-section calculates the n-th temperature change based on the (nxe2x88x921)th temperature change, the lapse time t and the heat value E.
In still another embodiment of the invention, the n-th temperature change is represented by expression (1) below or an approximate expression of expression (1):
T(n)=exp{xe2x88x92t/xcfx84}xc2x7T(nxe2x88x921)+kxc2x7Exe2x80x83xe2x80x83(1)
where T(n) denotes the n-th temperature change, T(nxe2x88x921) denotes the (nxe2x88x921)th temperature change, xcfx84 denotes a time constant, and k denotes a coefficient.
In still another embodiment of the invention, the n-th temperature change is represented by expression (2) below:
T(n)=[1xe2x88x92{t/xcfx84}]xc2x7T(nxe2x88x921)+kxc2x7Exe2x80x83xe2x80x83(2)
where T(n) denotes the n-th temperature change, T(nxe2x88x921) denotes the (nxe2x88x921)th temperature change, xcfx84 denotes a time constant, and k denotes a coefficient.
In still another embodiment of the invention, the heat value calculation sub-section calculates a moving distance of the head from the start position to the destination position and then calculates the heat value based on a function having the moving distance of the head as a variable.
In still another embodiment of the invention, the heat value calculation sub-section calculates the heat value based on a function having, as a variable, a change in an angular velocity of the disk in a time period during which the head moves from the start position to the destination position.
In still another embodiment of the invention, the disk driving section shifts an angular velocity of the disk to a destination angular velocity as the head moves from the start position toward the destination position, wherein when the head starts to move to a next destination position before the angular velocity of the disk has not reached the destination angular velocity, the heat value of the disk driving section and/or the head moving section is calculated based on a function having the lapse time counted by the timer as a variable.
In still another embodiment of the invention, the heat value calculation sub-section includes: a start angular velocity calculation portion for calculating a start angular velocity of the disk obtained when the head is located at the start position, a destination angular velocity calculation portion for calculating the destination angular velocity of the disk obtained when the head is located at the destination position; a reaching time calculation portion for calculating a reaching time required for the angular velocity of the disk to reach the destination angular velocity by being driven by the disk driving section, wherein the calculation is carried out based on the start angular velocity calculated by the start angular velocity calculation portion and the destination angular velocity calculated by the destination angular velocity calculation portion; and a comparison portion for selecting a shorter time between the reaching time calculated by the reaching time calculation portion and the lapse time counted by the timer, wherein the heat value of the disk driving section and/or the head moving section is calculated based on a function having the shorter time selected by the comparison portion as a variable.
In still another embodiment of the invention, the start angular velocity calculation portion calculates the start angular velocity based on expression (3) below or an approximate expression of expression (3):
xcfx89s(n)=xcfx89s(nxe2x88x921)+Cxc2x7tsxe2x80x83xe2x80x83(3)
where xcfx89s(n) denotes the start angular velocity at the point when the n-th temperature change is calculated, xcfx89s(nxe2x88x921) denotes the start angular velocity at the point when the (nxe2x88x921)th temperature change has been calculated, ts denotes the shorter value selected by the comparison portion, and C denotes a constant.
In still another embodiment of the invention, the heat value calculation portion calculates the heat value of the disk driving section and/or the head moving section based on expression (4) below:
E=Wxc2x7tsxe2x80x83xe2x80x83(4)
where E denotes the heat value, ts denotes the shorter time selected by the comparison portion, and W denotes a constant.
In still another embodiment of the invention, the temperature calculation section calculates the temperature change every time a head moving instruction for moving the head to a new destination position is issued.
In still another embodiment of the invention, the destination position in a head moving operation is set as a start position for the next head moving operation.
In still another embodiment of the invention, the control section sets an interval time t1 for driving the disk driving section and/or the head moving section intermittently when the temperature change calculated by the temperature calculation section exceeds a predetermined threshold.
In still another embodiment of the invention, the interval time t1 is calculated based on expression (5) below:
xe2x80x83ti=xcfx84xc2x7kxc2x7E/Thxe2x80x83xe2x80x83(5)
where xcfx84, k, and Th denote constants, and E denotes the heat value of the disk driving section and/or the head moving section.
In still another embodiment of the invention, the control section reduces the driving current applied to the disk driving section and/or the head moving section when the temperature change calculated by the temperature calculation section exceeds a predetermined threshold.
In still another embodiment of the invention, the control section includes a servo controller and a current instruction value limiting section, the servo controller generates a current instruction value for specifying the driving current applied to the disk driving section and/or the head moving section, and the current instruction value limiting section limits the current instruction value to a predetermined range when the temperature change calculated by the temperature calculation section exceeds the predetermined threshold.
In still another embodiment of the invention, a method for calculating the temperature change by the temperature calculation section is changed as the driving current applied to the disk driving section and/or the head moving section is reduced.
In still another embodiment of the invention, the control section reduces the driving current applied to the disk driving section and/or the head moving section when the temperature change calculated by the temperature calculate on section exceeds a predetermined threshold, and the temperature calculation section changes the constant C in expression (3) as the driving current applied to the disk driving section and/or the head moving section is reduced.
In still another embodiment of the invention the control section reduces the driving current applied to the disk driving section and/or the head moving section when the temperature change calculated by the temperature calculation section exceeds a predetermined threshold, and the temperature calculation section changes the constant W in expression (4) as the driving current applied to the disk driving section and/or the head moving section is reduced.
In still another embodiment of the invention, the disk device further includes a disk identification section for identifying the type of a disk, wherein a method for calculating the temperature change by the temperature calculation section, or a method for controlling the disk driving section and/or the head moving section by the control section is changed depending on the type of the disk identified by the disk identification sections.
In still another embodiment of the invention, operation of the temperature calculation section and/or the control section is permitted or prohibited depending on the type of the disk identified by the disk identification section.
In still another embodiment of the invention, the disk device further includes a rotation setting section for setting a rotational frequency or a rotation linear velocity of the disk, wherein a method for calculating the temperature change by the temperature calculation section, or a method for controlling the disk driving section and/or the head moving section by the control section is changed depending on the rotational frequency and/or the rotation linear velocity set by the rotation setting section.
In still another embodiment of the invention, the disk rotation setting section sets the rotational frequency or the rotation linear velocity of the disk depending on whether a disk rotation method is a CAV method, a CLV method, or a ZCLV method.
In still another embodiment of the invention, when the disk rotation method is the CAV method, the rotation setting section sets a fixed rotational frequency, and the operation of the temperature calculation section and/or the control section is prohibited.
In still another embodiment of the invention, when the disk rotation method is the ZCLV method and seeks are performed within a same zone, the rotation setting section sets a fixed rotational frequency, and the operation of the temperature calculation section and/or the control section is prohibited, and when the seeks extend to a different zone, the rotational frequency is changed by the rotation setting section, and the operation of the temperature calculation section and/or the control section is permitted.
In still another embodiment of the invention, the temperature calculation section calculates a temperature difference between portions of the disk.
Alternatively, the disk device of this invention includes: a disk driving section for rotating a disk; a head for recording and/or reproducing information on and/or from the disk; a head moving section for moving the head from a start position to a destination position; a temperature calculation section for calculating a temperature difference between portions of the disk; and a control section for controlling the disk driving section and/or the head moving section depending on the temperature difference calculated by the temperature calculation section.
In one embodiment of the invention, the control section reduces a driving current applied to the disk driving section when the temperature difference calculated by the temperature calculation section exceeds a predetermined threshold.
In another embodiment of the invention, the temperature calculation section includes a first temperature measurement element for detecting a temperature near an inner circumference of the disk and a second temperature measurement element for detecting a temperature near an outer circumference of the disk, and calculates a difference between the temperatures detected by the first and second temperature measurement elements.
Thus, the invention described herein makes possible the advantages of (1) providing a disk device requiring a reduced amount of arithmetic operation and thus reducing the burden on a control section, and (2) providing a disk device which performs temperature control capable of suppressing warping of a disk with high precision.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.